Looking to replace the stock shockwave brace, with a SBA3 brace. Does the pistol use a commercial or mil spec tube, so I can order the correct one ?

The answer to your question doesn't matter. To the best of my knowledge, the Shockwave brace uses it's own proprietary tube, so that'll come off with the brace itself to be replaced entirely by the SBA3 setup. Having said that, I guess the acutal buffer might be in question, but almost noooobody is using "commerical" buffer setup's in AR's these days.